Revealing the (3+2) and (2+2) Cycloaddition Reactivities of Wheland Intermediates

Wheland intermediates have long been confined to the classical electrophilic aromatic substitution reactions in addition to the limited types of nucleophilic interception or elimination reactions. Despite their structural resemblance to pentadienyl cations, allyl cations, and electron-deficient alkenes—all renowned cycloaddition partners—their potentials in cycloaddition reactions remained largely unexplored. Herein, we report the unprecedented (3+2) and (2+2) cycloaddition reactivities of Wheland intermediates. Under simple protic conditions, a wide range of modular N-homopropargyl-N-aryl propynamides facilely underwent dearomative cycloisomerizations, affording complex polycyclic three-dimensional architectures with high atom- and step-economy. These transformations were governed by both the hybridization nature of alkynes and the steric/electronic properties of the aniline rings, leading to divergent (3+2) and (2+2) reaction pathways. This work not only expanded the reactivity profile of Wheland intermediates but also provided a versatile strategy for dearomative functionalizations of arenes.